Systemsicherheit/Assignment 4 - Protokollsicherheit (Praxis)/proxy/proxymodules/size404.py

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2024-05-25 10:25:40 +02:00
#!/usr/bin/env python2
import os.path as path
import time
from distutils.util import strtobool
class Module:
def __init__(self, incoming=False, verbose=False, options=None):
# extract the file name from __file__. __file__ is proxymodules/name.py
self.name = path.splitext(path.basename(__file__))[0]
self.description = 'Change HTTP responses of a certain size to 404.'
self.incoming = incoming # incoming means module is on -im chain
self.size = 2392 # if a response has this value as content-length, it will become a 404
self.verbose = False
self.custom = False
self.rewriteall = False # will we block the first occurence?
self.firstfound = False # have we found the first occurence yet?
self.resetinterval = None # if we haven't found a fitting response in this many seconds, reset the state and set first to False again
self.timer = time.time()
if options is not None:
if 'size' in options.keys():
try:
self.size = int(options['size'])
except ValueError:
pass # use the default if you can't parse the parameter
if 'verbose' in options.keys():
self.verbose = bool(strtobool(options['verbose']))
if 'custom' in options.keys():
try:
with open(options['custom'], 'rb') as handle:
self.custom = handle.read()
except Exception:
print('Can\'t open custom error file, not using it.')
self.custom = False
if 'rewriteall' in options.keys():
self.rewriteall = bool(strtobool(options['rewriteall']))
if 'reset' in options.keys():
try:
self.resetinterval = float(options['reset'])
except ValueError:
pass # use the default if you can't parse the parameter
def execute(self, data):
contentlength = b'content-length: ' + bytes(str(self.size), 'ascii')
if data.startswith(b'HTTP/1.1 200 OK') and contentlength in data.lower():
if self.resetinterval is not None:
t = time.time()
if t - self.timer >= self.resetinterval:
if self.verbose:
print('Timer elapsed')
self.firstfound = False
self.timer = t
if self.rewriteall is False and self.firstfound is False:
# we have seen this response size for the first time and are not blocking the first one
self.firstfound = True
if self.verbose:
print('Letting this response through')
return data
if self.custom is not False:
data = self.custom
if self.verbose:
print('Replaced response with custom response')
else:
data = data.replace(b'200 OK', b'404 Not Found', 1)
if self.verbose:
print('Edited return code')
return data
def help(self):
h = '\tsize: if a response has this value as content-length, it will become a 404\n'
h += ('\tverbose: print a message if a string is replaced\n'
'\tcustom: path to a file containing a custom response, will replace the received response\n'
'\trewriteall: if set, it will rewrite all responses. Default is to let the first on through'
'\treset: number of seconds after which we will reset the state and will let the next response through.')
return h
if __name__ == '__main__':
print('This module is not supposed to be executed alone!')